Objective-C and HTTP Basic Authentication

For all the really nice stuff Objective-C lets you do on the iPhone, there are many, many holes left for very common tasks.

One of those tasks is Base64 encoding.

Base64 encoding is used to convert binary data into text that can be transmitted using HTTP (like, say, for embedding images in email) or for somewhat obfuscating user ids and passwords to be sent “in the clear” over HTTP (like for Basic Authentication).

Without much further ado, I present one of a gagillion implementations of Base64 encoding in C:

static char base64[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
"abcdefghijklmnopqrstuvwxyz"
"0123456789"
"+/";

int encode(unsigned s_len, char *src, unsigned d_len, char *dst)
{
unsigned triad;

for (triad = 0; triad < s_len; triad += 3)
{
unsigned long int sr;
unsigned byte;

for (byte = 0; (byte<3)&&(triad+byte<s_len); ++byte)
{
sr <<= 8;
sr |= (*(src+triad+byte) & 0xff);
}

sr <<= (6-((8*byte)%6))%6; /*shift left to next 6bit alignment*/

if (d_len < 4) return 1; /* error - dest too short */

*(dst+0) = *(dst+1) = *(dst+2) = *(dst+3) = '=';
switch(byte)
{
case 3:
*(dst+3) = base64[sr&0x3f];
sr >>= 6;
case 2:
*(dst+2) = base64[sr&0x3f];
sr >>= 6;
case 1:
*(dst+1) = base64[sr&0x3f];
sr >>= 6;
*(dst+0) = base64[sr&0x3f];
}
dst += 4; d_len -= 4;
}

return 0;

}

And here is how one may transmit a user id and password (using NSURLConnection) to establish a connection using Basic Authentication:

myApp.loginString    = (NSMutableString*)[[NSUserDefaults standardUserDefaults] stringForKey:kloginKey];
myApp.passwordString = (NSMutableString*)[[NSUserDefaults standardUserDefaults] stringForKey:kpasswordKey];

NSMutableString *dataStr = (NSMutableString*)[@"" stringByAppendingFormat:@"%@:%@", myApp.loginString, myApp.passwordString];

NSData *encodeData = [dataStr dataUsingEncoding:NSUTF8StringEncoding];
char encodeArray[512];

memset(encodeArray, '\0', sizeof(encodeArray));

// Base64 Encode username and password
encode([encodeData length], (char *)[encodeData bytes], sizeof(encodeArray), encodeArray);

dataStr = [NSString stringWithCString:encodeArray length:strlen(encodeArray)];
myApp.authenticationString = [@"" stringByAppendingFormat:@"Basic %@", dataStr];

// Create asynchronous request
NSMutableURLRequest * theRequest=(NSMutableURLRequest*)[NSMutableURLRequest requestWithURL:[NSURL URLWithString:@"https://www.somewebdomain.com"] cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:60.0];
[theRequest addValue:myApp.authenticationString forHTTPHeaderField:@"Authorization"];

NSURLConnection * theConnection=[[NSURLConnection alloc] initWithRequest:theRequest delegate:self];

[UIApplication sharedApplication].networkActivityIndicatorVisible = YES;
if (theConnection) {
receivedData = [[NSMutableData data] retain];
}
else {
[myApp addTextToLog:@"Could not connect to the network" withCaption:@"MyApp"];
}

Hopefully, this will help people get cracking that were having a hard time getting a handle on the fact that Objective-C is really C – albeit with funky class extensions.